than increasing performance. He also supported providing a steady level of funding for small-scale efforts to improve capabilities over the long term, with periodic reviews.

Todd Neill (Aerojet) provided very specific suggestions for the full list of launch propulsion technologies. In particular, he mentioned that NASA should move toward HTPB (hydroxy-terminated polybutadiene) propellants for solids, develop a nozzle extension for hydrogen engines and develop a new hydrocarbon boost engine. He saw little benefit to either hybrid propulsion systems or advanced propellants (besides the previously mentioned HTPB).

In the discussion session a few members of the audience suggested that hybrid propulsion systems should be high priority. They argued that hybrid systems have improved significantly in recent years, suggesting that they have higher efficiency than solid propulsion system, that they are less complex than liquid engines, and they are easy to manufacture and operate. There was also a discussion on the IHPRPT program as a model for propulsion technology development, with some suggesting that is a good program for attracting bright talent and developing new tools. Others criticized IHPRPT for starting with too much of a focus on improving performance, with not enough attention to cost reduction. One speaker disagreed that increasing launch rates is the best solution for reducing costs, suggesting that mission payloads could generally be repackaged in such a way to significantly increase the national launch rate. When asked what technologies would help improve affordability, various speakers mentioned improved materials, manufacturing, and health monitoring, and they cautioned that industry’s ability to invest in these technologies as they pertain to launch vehicles is constrained by high costs and low production rates.

Session 4: Launch Vehicle Manufacturers

Bernard Kutter (United Launch Alliance) started the session with launch vehicle manufacturers by emphasizing some of the points made earlier in the day. These include increased flight rates as a key to reducing cost and investing in cost reduction and operability instead of performance. Kutter noted that numerous attempts in the past 30 years to develop revolutionary systems had failed. He also said that it is unclear if reusability will show economic benefit. One technology he supported was integrated vehicle fluids, which would use primary engine propellants to serve the needs of auxiliary vehicle systems that currently use other fluids. Given the uncertainty in the future optimum vehicle configuration, he favored making technology investments in crosscutting technologies with broad applicability.

Gwynne Shotwell (SpaceX) reviewed the history of SpaceX. She believes that the highest priority propulsion technology would be a hydrocarbon boost engine with a thrust on the order of 1.5 million pounds or greater. Such an engine could support a NASA super heavy lift vehicle as well as smaller commercial launch systems. She suggested that this engine should be developed through a public-private partnership using a fixed price competition similar to the one NASA used for its Commercial Orbital Transportation Services program. This approach gives industry the flexibility and the incentives to produce optimum solutions.

John Steinmeyer (Orbital) agreed that a new high-thrust hydrocarbon boost engine should be the highest priority launch development. He suggested that the current Russian engines could be used as starting points, with the goal of a developing a propulsion system that could support the proposed NASA super heavy lift vehicle, smaller commercial launchers, and the proposed Air Force RBS. He asserted that the recent U.S. industrial space policy has hampered emerging technology through lack of focus and constancy. He said that new efforts should be properly funded and coordinated programs that capitalize on past developments and strategic, focused investments.

In the discussion session the hydrocarbon engine was further discussed with several speakers endorsing it as the best path forward for a super heavy lift system, especially if it were also used in other launch vehicles to reduce costs. Some speakers said that two competing engines should be developed to foster competition, but others countered that the market might be too small to support two vendors.


Bulman, M.J., and Siebenhaar, A. 2011. Combined cycle propulsion: Aerojet innovations for practical hypersonic vehicles. AIAA Paper 20112397. American Institute of Aeronautics and Astronautics, Reston, Va.

Eklund, D.R., Boudreau, A.H., and Bradford, J.E. 2005. A turbine-based combined cycle solution for responsive space access. AIAA Paper 2005-4186. American Institute of Aeronautics and Astronautics, Reston, Va.

Hampsten, K.R., and Hickman, R.A. 2010. Next Generation Air Force Spacelift. AIAA Paper 2010-8723. American Institute of Aeronautics and Astronautics, Reston, Va

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement